MAGNETIC RESONANCE IMAGING MEDICAL DEVICES AND ASSOCIATED METHODS - Patent application

Abstract

To provide medical devices useful in interventional procedures performed under magnetic resonance imaging.SOLUTION: A medical devices 100 useful in interventional procedures performed under magnetic resonance imaging (MRI) comprises a body member 110, and a marker 124, 126, 128, 130 formed of work-hardened stainless steel attached to the body member. The stainless steel of the marker has an ultimate tensile strength of about 100 KSI to about 225 KSI. The marker can be attached to the body member in a manner of working the stainless steel or in a manner of not working the stainless steel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 691,605, filed June 28, 2018. This related application is incorporated by reference in its entirety into this disclosure.

[0002] The present disclosure relates generally to the field of medical devices. More particularly, the present disclosure relates to medical devices useful in magnetic resonance imaging (MRI) equipment and techniques, methods of manufacturing medical devices useful in MRI equipment and techniques, medical imaging methods, and methods of performing interventional medical procedures. [Background technology]

[0003] Interventional magnetic resonance is an emerging field. The widespread use of MRI-based interventional procedures depends on several factors, including the availability of markers that can be used to indicate the location and other attributes of medical devices during interventional procedures. The prior art contains examples of markers suitable for use with MRI. For example, markers comprising iron oxide particles mixed into adhesives such as cyanoacrylate, epoxy resin, or UV-curable adhesives have been described. Associating these markers with medical devices is often laborious and difficult to reproduce consistently, making medical devices containing them and the interventional procedures they are intended to support unreliable and largely unacceptable by medical professionals. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, there is a need for new medical devices useful in MRI equipment and techniques, methods of manufacturing medical devices, imaging methods, and methods of performing interventional medical procedures. [Means for solving the problem]

[0005] Described herein are various medical devices, methods of manufacturing medical devices, imaging methods, and methods of performing interventional medical procedures.

[0006] The example medical device comprises a body member and a marker attached to the body member, the marker comprising work-hardened stainless steel.

[0007] Another example medical device includes a body member having a proximal end and a distal end and a stainless steel marker attached to the body member, the stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI. Another example medical device includes a body member having a proximal end and a distal end and a stainless steel marker attached to the body member, the stainless steel marker having an ultimate tensile strength of about 150 KSI to about 200 KSI. Another example medical device includes a body member having a proximal end and a distal end and a stainless steel marker attached to the body member, the stainless steel marker having an ultimate tensile strength of about 170 KSI to about 200 KSI. Another example medical device includes a body member having a proximal end and a distal end and a stainless steel marker attached to the body member, the stainless steel marker having an ultimate tensile strength of about 172 KSI to about 197 KSI. Another example medical device includes a body member having a proximal end and a distal end and a stainless steel marker attached to the body member, the stainless steel marker having an ultimate tensile strength of about 187 KSI to about 191 KSI. Another example medical device includes a body member having a proximal end and a distal end, and a stainless steel marker attached to the body member, the stainless steel marker having an ultimate tensile strength of about 189 KSI.

[0008] Another example medical device comprises a body member and a marker attached to the body member, the body member comprising an elongated rod, the marker comprising a stainless steel tubular member defining an inner lumen and having an ultimate tensile strength of about 100 KSI to about 225 KSI, and the marker is disposed around the elongated rod such that the elongated rod extends through the inner lumen of the marker.

[0009] Another example medical device includes a body member and a marker, the body member comprising a tubular member having a wall member having a thickness and defining a body lumen, the wall member defining a passageway extending within the thickness of the wall member, the marker comprising a stainless steel plug and having an ultimate tensile strength of about 100 KSI to about 225 KSI, and the marker is disposed within the passageway.

[0010] Another example medical device comprises a body member and a marker, the body member comprising a tubular member having a wall member having a thickness and defining a body lumen, the wall member defining a passageway extending through the entire thickness of the wall member, the marker comprising a stainless steel plug and having an ultimate tensile strength of about 100 KSI to about 225 KSI, and the marker disposed within the passageway.

[0011] Another example medical device includes a body member having a proximal end and a distal end, the body member including a cannula defining a lumen and a distal tip and having a cutting edge at the distal end, a hub member disposed at the proximal end of the body member, the cannula including a wall having opposed inner and outer surfaces, a wall thickness extending between the inner and outer surfaces, a passage extending partially through the wall thickness from one of the inner and outer surfaces, and a marker comprising a stainless steel plug and having an ultimate tensile strength of about 100 KSI to about 225 KSI disposed within the passage.

[0012] Another example medical device includes a body member having a proximal end and a distal end, the body member including a cannula defining a lumen and a distal tip and having a cutting edge at the distal end, a hub member disposed at the proximal end of the body member, the cannula including a wall having opposed inner and outer surfaces, a wall thickness extending between the inner and outer surfaces, a passageway extending through the entire thickness of the wall from the inner surface to the outer surface, and a marker disposed within the passageway, the marker including a stainless steel plug and having an ultimate tensile strength of about 100 KSI to about 225 KSI.

[0013] Another example medical device includes a first body member and a second body member associated with the first body member, wherein a first stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI is attached to the first body member and a second stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI is attached to the second body member.

[0014] Another example medical device includes a first body member having an elongated member and a second body member having a tubular member, the first body member being slidably disposed within the lumen of the second body member, a first stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI attached to the first body member, and a second stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI attached to the second body member.

[0015] An example method for manufacturing a medical device includes the steps of selecting a medical device precursor having a body member with a proximal end and a distal end; selecting a marker stock member formed from annealed stainless steel; separating a portion of the marker stock member from the remainder of the marker stock member to form a marker comprising annealed stainless steel; and attaching the marker to the body member in a manner that works the stainless steel of the marker, such that the marker comprises work-hardened stainless steel when the attaching step is complete.

[0016] Another example method of manufacturing a medical device includes selecting a medical device predecessor having a body member with a proximal end and a distal end; selecting a marker stock member formed from stainless steel; separating a portion of the marker stock member from the remainder of the marker stock member to form a marker; identifying a desired ultimate tensile strength for the marker; cold working the marker until it has a marker ultimate tensile strength that is substantially the same as the ultimate ultimate tensile strength; and attaching the marker to the body member in a manner that does not substantially work the stainless steel of the marker, such that upon completion of the attaching step, the marker has an ultimate tensile strength that is substantially the ultimate maximum tensile strength.

[0017] Another example method of manufacturing a medical device includes selecting a medical device predecessor having a body member with a proximal end and a distal end; selecting a marker stock member formed from stainless steel having a starting maximum tensile strength; separating a portion of the marker stock member from the remainder of the marker stock member to form a marker; identifying a desired final maximum tensile strength for the marker; cold working the marker until it has a marker maximum tensile strength that is greater than the starting maximum tensile strength but less than the final maximum tensile strength; and attaching the marker to the body member in a manner that works the stainless steel of the marker, such that upon completion of the attaching step, the marker has a maximum tensile strength that is substantially the final maximum tensile strength.

[0018] Another example method of manufacturing a medical device includes selecting a medical device precursor having a body member with proximal and distal ends, a first surface, a second surface, a thickness, and defining a passageway extending from the first surface toward the second surface; selecting an annealed stainless steel plug; cold working the plug to form a marker; and forcing the marker into the passageway.

[0019] Another example method of manufacturing a medical device includes selecting a medical device precursor having a body member having proximal and distal ends, a first surface, a second surface, a thickness, and defining a passageway extending from the first surface toward the second surface; selecting an annealed stainless steel plug; cold working the plug to form a marker having an ultimate tensile strength of about 100 KSI to about 225 KSI; and forcing the marker into the passageway.

[0020] Another example method for manufacturing a medical device includes separating a portion of marker stock from a marker stock member comprising annealed stainless steel, cold working the portion to form a marker having an ultimate tensile strength of about 100 KSI to about 225 KSI, and attaching the marker to a body member of a medical device precursor to form the medical device.

[0021] Another example method for manufacturing a medical device includes separating a portion of marker stock from a marker stock member comprising annealed stainless steel, cold working the portion to form a marker having an ultimate tensile strength of about 100 KSI to about 225 KSI, and attaching the marker to a body member of a medical device precursor in a manner that increases the ultimate tensile strength of the marker to form said medical device, wherein the marker has an ultimate tensile strength of about 100 KSI to about 225 KSI.

[0022] Another example method for manufacturing a medical device includes separating a portion of marker stock from a marker stock member comprising annealed stainless steel, cold working the portion to form a marker having an ultimate tensile strength of less than about 200 KSI, and attaching the marker to a body member of a medical device precursor in a manner that increases the ultimate tensile strength of the marker to form said medical device, wherein the marker has an ultimate tensile strength of greater than about 200 KSI.

[0023] An example imaging method includes selecting a medical device having a body member with a proximal end and a distal end, the medical device including a marker formed from work-hardened stainless steel; advancing the distal end of the medical device to a first position within a patient's body canal until the marker is positioned at a second position within the body canal; scanning a portion of the body canal including the first and second positions within the body canal using a magnetic resonance scanner; obtaining a magnetic resonance image of the portion of the body canal such that the image includes an artifact indicative of the presence of the marker within the portion of the body canal; and withdrawing the medical device from the body canal.

[0024] Another example imaging method includes selecting a medical device having a body member with a proximal end and a distal end, the medical device including a stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI; advancing the distal end of the medical device to a first location within a patient's body canal until the marker is positioned at a second location within the body canal; scanning a portion of the body canal including the first and second locations within the body canal using a magnetic resonance scanner; obtaining a magnetic resonance image of the portion of the body canal such that the image includes an artifact indicative of the presence of the marker within the portion of the body canal; and withdrawing the medical device from the body canal.

[0025] An example method for performing an interventional medical procedure includes selecting a medical device having a body member with a proximal end and a distal end, the medical device including a marker formed from work-hardened stainless steel; advancing the distal end of the medical device to a first position within a patient's body canal until the marker is located at a second position within the body canal; acquiring a magnetic resonance image of a portion of the body canal including the second position while the marker is located at the second position within the body canal; viewing an artifact created by the presence of the marker in the image while acquiring the magnetic resonance image; manipulating the medical device based on the position of the artifact relative to the body canal; and withdrawing the medical device from the body canal.

[0026] Another example method of performing an interventional medical procedure includes selecting a medical device having a body member with a proximal end and a distal end, the medical device including a stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI; advancing the distal end of the medical device to a first location within a patient's body canal until the marker is located at a second location within the body canal; acquiring a magnetic resonance image of a portion of the body canal that includes the second location while the marker is located at the second location within the body canal; viewing an artifact created by the presence of the marker in the image while acquiring the magnetic resonance image; manipulating the medical device based on the location of the artifact relative to the body canal; and withdrawing the medical device from the body canal.

[0027] Another example method of performing an interventional medical procedure includes selecting a medical device having a body member with a proximal end and a distal end, the medical device including a marker formed from work-hardened stainless steel; advancing the distal end of the medical device to a first location within a patient's body canal until the marker is located at a second location within the body canal; acquiring a magnetic resonance image of a portion of the body canal including the second location while the marker is located at the second location within the body canal; determining a location of a portion of the medical device within the body canal based at least in part on an artifact produced by the presence of the marker in the image while acquiring the magnetic resonance image; manipulating the medical device within the body canal; and withdrawing the medical device from the body canal.

[0028] Another example method of performing an interventional medical procedure includes selecting a medical device having a body member with a proximal end and a distal end, the medical device including a stainless steel marker having an ultimate tensile strength of about 100 KSI to about 225 KSI; advancing the distal end of the medical device to a first location within the patient's body vessel until the marker is located at a second location within the body vessel; acquiring a magnetic resonance image of a portion of the body vessel including the second location while the marker is located at the second location within the body vessel; determining a location of a portion of the medical device within the body vessel based at least in part on an artifact produced by the presence of the marker in the image while acquiring the magnetic resonance image; manipulating the medical device within the body vessel; and withdrawing the medical device from the body vessel.

[0029] A further understanding of the claimed invention can be obtained by reviewing the detailed description of selected example medical devices, methods of manufacturing medical devices, imaging methods, and methods of performing interventional medical procedures with reference to the accompanying drawings. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a partially cut-away perspective view of an example medical device. [Figure 2] 1 is a partially cut-away cross-sectional view of another example medical device. [Figure 3] 1A-1C are perspective views of example markers suitable for use in medical devices, according to embodiments. [Figure 4] FIG. 1 is a perspective view of another example medical device. [Figure 5] FIG. 5 is an enlarged view of the distal end of the medical device shown in FIG. 4. [Figure 5A] 5 is an enlarged view of the distal end of the medical device shown in FIG. 4 before markers are attached to the body member of the medical device. [Figure 6] 1 is a schematic diagram of an example method for manufacturing a medical device. [Figure 7] 1 is a schematic diagram of another example method for manufacturing a medical device. [Figure 8]1 is a schematic diagram of another example method for manufacturing a medical device. [Figure 9] 1 is a schematic diagram of another example method for manufacturing a medical device. [Figure 10] 1 is a schematic diagram of another example method for manufacturing a medical device. [Figure 11] 1 is a schematic diagram of another example method for manufacturing a medical device. [Figure 12] FIG. 1 is a schematic diagram of an example imaging method. [Figure 13] FIG. 10 is a schematic diagram of another example imaging method. [Figure 14] 1 is a schematic diagram of an example method for performing an interventional medical procedure. [Figure 15] FIG. 1 is a schematic diagram of another example method for performing an interventional medical procedure. [Figure 16] FIG. 1 is a schematic diagram of another example method for performing an interventional medical procedure. [Figure 17] FIG. 1 is a schematic diagram of another example method for performing an interventional medical procedure. [Figure 18A] MRI images of a first Nitinol rod with a set of annealed 0.5 mm stainless steel markers attached and a second Nitinol rod with a set of unannealed 0.5 mm stainless steel markers attached. Each arrow indicates an artifact from one marker from each set of markers. [Figure 18B] MRI images of a first Nitinol rod with a set of annealed 1.0 mm stainless steel markers attached and a second Nitinol rod with a set of unannealed 1.0 mm stainless steel markers attached. Each arrow indicates an artifact from one marker from each set of markers. [Figure 18C] MRI images of a first Nitinol rod with a set of annealed 1.5 mm stainless steel markers attached and a second Nitinol rod with a set of unannealed 1.5 mm stainless steel markers attached. Each arrow indicates an artifact from one marker from each set of markers. DETAILED DESCRIPTION OF THE INVENTION

[0031] The following detailed description and accompanying drawings describe and illustrate various example medical devices, methods of manufacturing medical devices, medical imaging methods, and methods of performing interventional medical procedures. These example descriptions and illustrations are provided to enable those skilled in the art to manufacture and use medical devices, perform methods of manufacturing medical devices, perform medical imaging methods, and perform methods of performing interventional medical procedures in accordance with embodiments of the invention. They are not intended to limit in any way the scope of the invention or the protection sought. The invention can be practiced or carried out in various ways, and the examples described and illustrated herein are merely selected examples of these various ways and are not intended to be exhaustive.

[0032] The term "attached" as used herein refers to one member being fixed to another member such that the members do not completely separate from one another during use in accordance with the intended use of the article containing the members in their attached configuration.

[0033] The term "KSI" is used herein as a unit of measure for quantifying the tensile strength of a material and refers to thousands of pounds per square inch, or kilopounds per square inch.

[0034] The term "plug" as used herein refers to a member having a size and configuration suitable for placement within a hole, cavity, passageway, or void in another member. The term does not require any particular size or configuration; the size and configuration of a particular plug will depend on the size and configuration of the hole, cavity, passageway, or void into which it is intended to be placed.

[0035] As used herein, the term "stainless steel" refers to a steel alloy having a minimum chromium content of 10.5% by mass.

[0036] As used herein, the term "work hardened stainless steel" and grammatically related terms refer to stainless steel that has been hardened by cold working.

[0037] Magnetically susceptible materials are typically avoided when developing medical devices for use in MRI equipment and techniques because they can be deflected by strong magnetic fields, such as the 1.5T and 3T fields used in conventional medical MRI scanners. The potential for radio frequency (RF) induction heating also presents challenges to the use of these materials in MRI equipment and techniques. Furthermore, these materials cause visual artifacts in MRI scans that can obscure the field of view and tissues and / or body structures of interest within the field of view, reducing the overall value of the procedure.

[0038] However, the present inventors have discovered that by controlling the magnetic permeability and optionally other physical attributes of the stainless steel elements used in the manufacture of medical devices, stainless steel markers can cause useful visual artifacts in MRI images. Instead of reducing the overall value of the MRI scan, these visual artifacts dramatically improve the value of the scan by enabling the use of various interventional medical devices and methods. Furthermore, the present inventors have discovered that by controlling the ultimate tensile strength of the stainless steel elements used in the manufacture of medical devices, markers can be incorporated into the medical device that have a magnetic permeability that causes useful visual artifacts in MRI images, as opposed to visual artifacts that adversely affect the usefulness of the MRI images, thereby making the medical device more effective and desirable for MRI techniques. Furthermore, the present inventors have discovered that controlling the amount of processing applied to the stainless steel elements used in the manufacture of medical devices, i.e., the degree of cold working performed on the stainless steel, enables a useful and efficient method of manufacturing medical devices that are useful in MRI equipment and techniques. Furthermore, controlling the amount of processing applied to the stainless steel elements used in the manufacture of medical devices enables useful imaging methods and methods of performing interventional medical procedures.

[0039] FIG. 1 illustrates a first example medical device 100. In this example, medical device 100 is a guidewire. The medical device includes a body member 110 having a proximal end 112 and a distal end 114. Body member 110 includes a mandrel 116 and a reinforcing member 118. Mandrel 116 and reinforcing member 118 each extend from body member proximal end 112 to body member distal end 114. Reinforcing member 118 defines a lumen 120. Mandrel 116 is disposed within lumen 120. A plurality of markers 122 are disposed along the axial length of body member 110. Thus, each marker of the plurality of markers 122 is circumferentially disposed around reinforcing member 118. Each marker of the plurality of markers is attached to body member 110. In the illustrated embodiment, the plurality of markers 122 includes a first marker 124, a second marker 126, a third marker 128, and a fourth marker 130. An outer sheath 132 is disposed over the stiffening member 118 and the plurality of markers 122.

[0040] The mandrel 116 may comprise any suitable mandrel. In the illustrated embodiment, the mandrel 116 comprises an elongated member formed from a nickel-titanium alloy.

[0041] The reinforcing member 118 may comprise any suitable material. In the illustrated embodiment, the reinforcing member comprises a tubular member defining a lumen 120 within which the mandrel 116 may be positioned. Additionally, the reinforcing member 118 may be formed from any suitable material, such as a polyamide or polyimide material.

[0042] Each marker of the plurality of markers 122 comprises work-hardened stainless steel. Furthermore, each marker of the plurality of markers 122 has properties that cause visual artifacts during an MRI procedure in which the medical device 100 is imaged. These visual artifacts can be used to determine the placement of the medical device 100 relative to other portions of an MRI image, such as the portion of a body canal through which the medical device 100 has been advanced. The inventors have determined that markers with certain properties cause visual artifacts, and that such visual artifacts have sizes and shapes that make them particularly useful in this regard. For example, the inventors have determined that markers having a maximum tensile strength of about 100 KSI to about 225 KSI cause particularly useful visual artifacts during an MRI procedure in which a medical device containing the marker is imaged. In fact, the inventors have determined that it is critical that the markers have a maximum tensile strength within this range in order for the medical devices and methods described herein to be useful with MRI equipment and techniques. Markers with a maximum tensile strength outside this range present an unacceptable probability that visual artifacts caused by the marker in an MRI scan will ultimately have a negative impact on the value of the scan. For example, visual artifacts may be so great that they obscure other portions of the image produced by the scan to an unacceptable degree or level. While markers having maximum tensile strengths outside this range produce unacceptable results, the inventors have determined that markers having maximum tensile strengths within a narrower range can produce visual artifacts that are as useful or better than markers having maximum tensile strengths of about 100 KSI to about 225 KSI. In fact, the inventors have determined that markers having maximum tensile strengths of about 150 KSI to about 200 KSI produce visual artifacts that are particularly useful during MRI procedures in which medical devices containing the markers are imaged. Furthermore, the inventors have determined that markers having maximum tensile strengths of about 170 KSI to about 200 KSI produce visual artifacts that are particularly useful during MRI procedures in which medical devices containing the markers are imaged.Furthermore, the inventors have determined that markers having a maximum tensile strength of about 172 KSI to about 197 KSI produce particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged. Furthermore, the inventors have determined that markers having a maximum tensile strength of about 187 KSI to about 191 KSI produce particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged. Furthermore, the inventors have determined that markers having a maximum tensile strength of about 189 KSI produce particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged.

[0043] The mass of each marker also contributes to visual artifacts caused by the marker during an MRI scan. However, it is important to balance the mass of each marker and the total mass of all markers in a medical device according to embodiments with performance considerations for the medical device, such as ease of handling, pushability, and torque transmission. The inventors have determined that markers having masses between about 0.05 mg and about 2.74 mg produce particularly useful visual artifacts. While markers having masses outside this range increase the likelihood that the markers will adversely affect the performance considerations described above, the inventors have determined that markers having masses within a narrower range can produce visual artifacts with the same or better usability than markers having masses between about 0.05 mg and about 2.74 mg. In fact, the inventors have determined that markers having masses between about 0.1 mg and about 1.37 mg produce particularly useful visual artifacts without adversely affecting the performance considerations of the medical device in any significant way. The inventors have determined that markers having a mass of about 0.15 mg to about 0.685 mg produce particularly useful visual artifacts without adversely affecting the performance considerations of the medical device in any significant way.Furthermore, the inventors have determined that markers having a mass of about 0.15 mg produce particularly useful visual artifacts without adversely affecting the performance considerations of the medical device in any significant way.

[0044] In some embodiments, markers are incorporated into medical devices based on both ultimate tensile strength and mass considerations. In practice, the inventors have determined that markers having an ultimate tensile strength of about 100 KSI to about 225 KSI and a mass of about 0.34 mg to about 2.74 mg produce particularly useful visual artifacts during MRI procedures in which medical devices incorporating the markers are imaged. Furthermore, the inventors have determined that markers having an ultimate tensile strength of about 150 KSI to about 200 KSI and a mass of about 0.69 mg to about 2.05 mg produce particularly useful visual artifacts during MRI procedures in which medical devices incorporating the markers are imaged. Furthermore, the inventors have determined that markers having an ultimate tensile strength of about 170 KSI to about 200 KSI and a mass of about 0.69 mg to about 2.05 mg produce particularly useful visual artifacts during MRI procedures in which medical devices incorporating the markers are imaged. Furthermore, the present inventors have shown that a marker having a maximum tensile strength of about 172 KSI to about 197 KSI and a mass of about 0.69 mg to about 2.05 mg produces a particularly useful visual artifact during an MRI procedure in which a medical device containing the marker is imaged. Furthermore, the present inventors have shown that a marker having a maximum tensile strength of about 187 KSI to about 191 KSI and a mass of about 0.69 mg to about 2.05 mg produces a particularly useful visual artifact during an MRI procedure in which a medical device containing the marker is imaged. Furthermore, the present inventors have shown that a marker having a maximum tensile strength of about 189 KSI and a mass of about 1.37 mg produces a particularly useful visual artifact during an MRI procedure in which a medical device containing the marker is imaged.

[0045] Spatial and other considerations can guide the selection of a suitable mass and maximum tensile strength for a particular marker in a particular medical device. For example, the inventors have determined that selecting a marker having a mass in the lower portion of the range of about 0.05 mg to about 2.74 mg, e.g., less than about 1 mg, but in the upper portion of the range of about 100 KSI to about 225 KSI, e.g., greater than about 175 KSI, can produce particularly useful visual artifacts, especially for markers in medical devices where large markers may be difficult to place. For example, the inventors believe that a marker having a mass of about 0.15 mg and a maximum tensile strength of about 189 KSI would produce a useful visual artifact as a plug placed at the distal end of a guidewire or in the wall of a cannula. As discussed in more detail below, the overall length of the marker also contributes to the visual artifact caused by the marker during an MRI scan. In this particular example, the inventors have determined that a length of about 0.4 mm provides a marker large enough to be conveniently handled during manufacturing, but not so large as to cause dephasing in the blood, as discussed below. Conversely, the inventors have determined that selecting a marker having a mass in the upper portion of the range of about 0.05 mg to about 2.74 mg, e.g., greater than about 1 mg, but having an ultimate tensile strength in the lower portion of the range of about 100 KSI to about 225 KSI, e.g., less than about 197 KSI, can cause visual artifacts that are particularly useful for markers in medical devices where small markers may be difficult to position or where handling of small markers during manufacturing is a paramount concern.

[0046] It should be noted that a group of closely related markers can be used to achieve visual artifacts similar to those caused by a single marker. For example, three markers having a desired maximum tensile strength can be attached to a medical device in a manner that forms a group of closely related markers on the medical device so that the markers, as a group, cause the desired visual artifact during an MRI scan. Any suitable number of markers can be used in this type of group, including two markers, more than two markers, three markers, multiple markers, four markers, five markers, and more than five markers. Markers can also be selected based on their contribution to the desired overall mass of the marker load. For example, in the example recited above, where it is desirable to have markers with a mass of approximately 0.15 mg and a maximum tensile strength of approximately 189 KSI, a marker group including three separate markers, each with a mass of approximately 0.05 mg and a maximum tensile strength of approximately 189 KSI, can be used in place of a single marker with a mass of approximately 0.15 mg and a maximum tensile strength of approximately 189 KSI. When marker groups are attached to a medical device in a manner that forms a group of closely related markers, they are expected to cause visual artifacts in an MRI scan similar to those caused by a single marker. In these embodiments, it is important that the individual markers in a marker group are positioned relative to one another so that the group causes visual artifacts similar to those caused by a single marker. If the individual markers in a marker group are positioned too far from one another so that they are not closely related enough, the visual artifact caused by the group is likely to be a separate visual artifact that may obscure portions of the image obtained in the MRI scan.

[0047] The overall length of each marker also contributes to visual artifacts caused by the marker during an MRI scan. However, similar to the mass considerations described above, it is important to balance the length of each marker and the overall length of all markers in a medical device according to embodiments with performance considerations, such as ease of handling, pushability, and torque transmission. Additionally, excessively long markers may result in, for example, blood dephasing. The inventors have found that markers having lengths of about 0.25 mm to about 2.0 mm produce particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged. Furthermore, the inventors have found that markers having lengths of about 0.5 mm to about 1.5 mm produce particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged. Furthermore, the inventors have found that markers having lengths of about 1.0 mm produce particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged. Furthermore, the inventors have determined that markers having a length of about 0.5 mm cause particularly useful visual artifacts during MRI procedures in which medical devices containing the markers are imaged. The inventors have determined that markers having a length greater than 2.0 mm may cause visual artifacts during MRI procedures that are too large to be useful for certain applications.

[0048] Each marker of the plurality of markers 122 can be attached to the body member 110 in any suitable manner. In the illustrated embodiment, each of the markers 124, 126, 128, and 130 is attached to the body member 110 in a manner that does not alter the stainless steel. In other words, each of the markers 124, 126, 128, and 130 is attached to the body member 110 in a manner that does not increase the ultimate tensile strength of the stainless steel in the marker. This arrangement is considered suitable when the markers include work-hardened stainless steel having a desired final ultimate tensile strength and magnetic permeability. For medical devices in which this arrangement is desirable, the markers can be attached to the body member in any suitable manner that does not alter the work-hardened stainless steel of the marker. In the illustrated embodiment, each of the markers 124, 126, 128, and 130 is attached to the body member 110 by an adhesive disposed between the marker and the reinforcing member 118. In these embodiments, any adhesive deemed suitable for inclusion in a medical device can be used.

[0049] Each marker of the plurality of markers 122 can have any suitable configuration. In the illustrated embodiment, each marker 124, 126, 128, 130 includes a tubular member defining a marker lumen. The tubular markers can be disposed around a portion of the body member 110 of the medical device 100. As shown in FIG. 1 , the tubular markers 124, 126, 128, 130 can be disposed around the stiffening member 118 such that each marker 124, 126, 128, 130 extends around the entire circumference of the stiffening member 118. Alternatively, markers defining a partial circumference can be disposed around the body member of a medical device embodiment such that each marker extends around only a portion of the circumference of the body member.

[0050] Any suitable number of markers can be used in medical devices according to embodiments. While the first example medical device includes four markers 124, 126, 128, and 130, it should be understood that medical devices according to embodiments can include any number of markers deemed suitable for the intended use of the particular medical device. Examples of suitable numbers of markers to include in medical devices according to embodiments include one marker, two markers, more than two markers, three markers, multiple markers, four markers, five markers, six markers, seven markers, eight markers, nine markers, ten markers, and more than ten markers. Furthermore, in embodiments including two or more markers, the markers can be spaced apart from one another by any desired distance. However, because markers cause visual artifacts and their usefulness in medical devices is based on the production of these visual artifacts in MRI procedures, it is important to space the markers apart from one another by a distance that does not result in overlapping or nearly overlapping visual artifacts. If markers are spaced too closely together on a medical device, the visual artifacts caused by the individual markers may overlap or nearly overlap, thereby rendering the markers useless. When this occurs, the obscuring properties of the overlapping or nearly overlapping visual artifacts may outweigh any benefit caused by their presence. The inventors have determined that in a medical device having a first marker and a second marker, such as a guidewire shown as medical device 100 in FIG. 1, it is advantageous to space the first marker from the second marker by a distance of about 5 cm to about 100 cm. Furthermore, the inventors have determined that in a medical device having a first marker and a second marker, it is advantageous to space the first marker from the second marker by a distance of about 5 cm to about 10 cm.The inventors have further determined that in a medical device having a first marker and a second marker, it is advantageous to space the first marker from the second marker by a distance greater than about 10 cm. The inventors have further determined that in a medical device having a first marker and a second marker, it is advantageous to space the first marker from the second marker by a distance of about 10 cm. The inventors have further determined that in a medical device having a first marker and a second marker, it is advantageous to space the first marker from the second marker by a distance greater than about 5 cm. The inventors have further determined that in a medical device having a first marker and a second marker, it is advantageous to space the first marker from the second marker by a distance of about 5 cm. The inventors have determined that markers spaced less than about 5 cm apart may cause visual artifacts that are too close to each other to be useful for certain applications.

[0051] Also, in a medical device having three markers, the first marker can be spaced a first distance from the second marker, and the second marker can be spaced a second distance from the third marker. The first and second distances can be the same or different. The inventors have determined that regular spacing between markers in certain embodiments of a medical device can be advantageous because the markers are visualized in MRI through the visual artifacts they cause. Therefore, a regular pattern of artifacts can improve the usefulness of the markers in these procedures. Nevertheless, irregular spacing between some or all markers in certain embodiments of a medical device including multiple markers can be used as well. For example, in the illustrated embodiment, first marker 124 and second marker 126 are spaced apart from one another by a first distance 140, second marker 126 and third marker 128 are spaced apart from one another by a second distance 150, and third marker 128 and fourth marker 130 are spaced apart from one another by a third distance 160. Each of first distance 140, second distance 150, and third distance 160 is different from the other distances.

[0052] Outer sheath 132 can have any suitable configuration. For example, in the illustrated embodiment, outer sheath 132 includes a polymer sheath disposed over stiffening member 118 such that it extends over stiffening member 118 and plurality of markers 122. Alternatively, outer sheath 132 can include a coating or other suitable configuration. For example, outer sheath 132 can include a polymer coating applied to stiffening member 118 or another element that forms a jacket over the element.

[0053] FIG. 2 illustrates a second example medical device 200. In this example, medical device 200 is a segmented guidewire. Medical device 200 includes a body member 210 having a proximal end 212 and a distal end 214. Body member 210 includes a plurality of rods 216 and a plurality of connectors 218. Each connector of plurality of connectors 218 is disposed between and connects a pair of adjacent rods of plurality of rods 216. A plurality of markers 222 are disposed along the axial length of body member 210. Each marker of plurality of markers 222 is circumferentially disposed around one of plurality of rods 216. Thus, each marker of plurality of markers 222 is attached to body member 210. In the illustrated embodiment, plurality of markers 222 includes a first marker 224, a second marker 226, a third marker 228, and a fourth marker 230. An outer sheath 232 is disposed over the plurality of rods 216, the plurality of connectors 218 and the plurality of markers 222.

[0054] Each of the plurality of rods 216 advantageously comprises a metal, such as Nitinol or another alloy. Importantly, however, the axial length of each of the plurality of rods 216 is sufficiently short so that the rod does not resonate during an MRI procedure. For example, for a medical device intended for use in a 1.5T MRI scanner, each rod should have an axial length that is less than 10 cm. For a medical device intended for use in a 3.0T MRI scanner, each rod should have an axial length that is less than 5 cm. Each connector of the plurality of connectors 218 advantageously comprises a non-metallic insulating material, such as a polymeric material. Alternatively, each connector of the plurality of connectors 218 can comprise a material coated with a non-metallic insulating material. Alternatively, in some embodiments, the rod can comprise a metal coated with a non-metallic insulating material, and the connector can comprise a metal, a non-metallic material, or a metal coated with a non-metallic insulating material.

[0055] In the illustrated embodiment, each of the markers 224, 226, 228, and 230 is attached to the body member 210 in a manner that works the stainless steel from which the marker is formed so that, in the final medical device 200, each of the markers 224, 226, 228, and 230 comprises work-hardened stainless steel. In other words, each of the markers 224, 226, 228, and 230 is attached to the body member 210 in a manner that increases the ultimate tensile strength of the stainless steel in the marker. This arrangement may be preferred when the markers are formed from stainless steel that does not have the final desired ultimate tensile strength and magnetic permeability. For medical devices in which this arrangement is desirable, the markers can be attached to the body member in any suitable manner that works the stainless steel of the markers so that, in the final medical device, each of the markers comprises work-hardened stainless steel. Any cold working process may be used, including crimping, swaging, hammering, pressing, pinning, and dimpling. In the illustrated embodiment, each of the markers 224, 226, 228, 230 is crimped onto one of the rods 216 of the body member 210. Other attachments to the markers 224, 226, 228, 230 are possible. For example, one or more of the markers 224, 226, 228, 230 can be attached to the body member 210 at the junction of the rod 216 and the connector 218.

[0056] The medical device 200 of this embodiment includes regular spacing between the markers 224, 226, and 228. As shown in FIG. 2 , the first marker 224 and the second marker 226 are spaced apart from one another by a first distance 240, and the second marker 226 and the third marker 228 are spaced apart from one another by a second distance 250. The first distance 240 is the same as the second distance 250. The third marker 228 and the fourth marker 230 are spaced apart from one another by a third distance 260, which is different from the first distance 240 and the second distance 250. In the illustrated embodiment, the third distance 260 is greater than the first distance 240 and the second distance 250.

[0057] The first example medical device 100 includes only markers 124, 126, 128, 130, i.e., markers 124, 126, 128, 130 attached to the body member 110 of the medical device 100 in a manner that does not alter the stainless steel of the individual markers 124, 126, 128, 130, and the second example medical device 200 includes only markers 224, 226, 228, 230, i.e., markers 224, 226, 228, 230 attached to the body member 210 of the medical device 200 in a manner that does not alter the stainless steel of the individual markers 224, 226, 228, 230. While the medical device includes only markers 224, 226, 228, and 230 attached to the body member of the medical device, it should be noted that certain embodiments of the medical device may include one or more markers, i.e., one or more markers attached to the body member of the medical device in a manner that does not alter the stainless steel of the marker or markers, and may also include one or more markers, i.e., one or more markers attached to the body member of the medical device in a manner that alters the stainless steel of the marker or markers. In other words, certain embodiments of the medical device may include one or more markers, i.e., one or more markers attached to the body member of the medical device in a manner that does not increase the ultimate tensile strength of the stainless steel of the marker or markers, and may also include one or more markers, i.e., one or more markers attached to the body member of the medical device in a manner that increases the ultimate tensile strength of the stainless steel of the marker or markers. For example, certain embodiments of the medical device may include a first marker attached to the body member and a second marker crimped to the same or another body member of the medical device. This configuration may be useful in medical devices that include multiple body members, each of which may benefit from the presence of a marker that causes a useful visual artifact in MRI images.For example, a catheter having an elongate member, such as a dilator or other core member, slidably disposed within an outer sheath member can include one or more markers attached to the core member in a manner that adds to the stainless steel of the markers, and can also include one or more markers attached to the outer sheath member in a manner that does not add to the stainless steel of the markers. Of course, the reverse arrangement is also possible. For example, a catheter can include one or more markers attached to the core member in a manner that does not add to the stainless steel of the markers, and can also include one or more markers attached to the outer sheath member in a manner that adds to the stainless steel of the markers.

[0058] FIG. 3 illustrates an example marker 300 suitable for use in medical devices according to embodiments. The marker is a short tubular member 310 having an outer surface 312 and defining a marker lumen 314. The marker lumen 314 for the illustrated marker defines a substantially circular cross-sectional shape. However, it should be noted that the marker lumen for markers used in medical devices according to embodiments can define different cross-sectional shapes. For example, in medical device embodiments in which the marker is attached to a body member by machining the stainless steel of the marker, the marker lumen can define a substantially oval cross-sectional shape or a substantially rectangular cross-sectional shape. In these embodiments, a marker having a lumen defining a substantially circular cross-sectional shape, such as marker 300 illustrated in FIG. 3, can be placed in a body member of a medical device and then attached to the body member using techniques such as machining the stainless steel of the marker, crimping or swaging the marker to the body member, or the like. Also, while the illustrated marker 300 defines an angled tubular member, it should be noted that other tubular configurations are suitable for use as markers in medical devices according to embodiments of the present invention. For example, straight, substantially straight, and curved tubular members can be used.

[0059] 4, 5, and 5A show a third example medical device 400. In this example, the medical device 400 is a needle. The medical device 400 includes a body member 410 having a proximal end 412 and a distal end 414. In this embodiment, the body member is a cannula 416 defining a lumen 418 and a distal tip 420, with a cutting edge 422 at the distal end 414. A hub member 424 is disposed at the proximal end 412 of the body member 410. As best shown in FIG. 5, a marker 450 is attached to the cannula 416 and, therefore, to the body member 410.

[0060] As best shown in FIG. 5, the cannula 416 includes a wall 426 having opposed inner and outer surfaces 428 and 430. A wall thickness extends between the inner and outer surfaces 428 and 430. As best shown in FIG. 5A, which shows the distal end of the medical device 400 without markers 450, a passageway 432 extends through the entire thickness of the wall 426 from the inner surface 428 to the outer surface 430. Alternatively, the passageway can extend only partially through the thickness of the wall 426, from the inner surface 428 toward the outer surface 430 or from the outer surface 430 toward the inner surface 428.

[0061] In this embodiment, marker 450 is a plug disposed within passageway 432. As best shown in FIG. 5 , marker 450 is flush with inner surface 428 and outer surface 430. In this embodiment, marker 450 is attached to body member 410 by processing the stainless steel of the marker so that in the final medical device 400, marker 450 comprises work-hardened stainless steel. In this embodiment, marker 450 is pressed into passageway 432. The friction fit between wall 426 and marker 450 and the force required to press marker 450 into passageway 432 may be sufficient to achieve the desired ultimate tensile strength for the stainless steel of marker 450 and its attachment to body member 410. Additional fastening may be used if desired. For example, marker 450 may be laser welded to wall 426 to secure marker 450 within passageway 432.

[0062] In other medical device embodiments, one or more filaments of cold-worked stainless steel having a known ultimate tensile strength are disposed within the medical device. For example, multiple filaments can be embedded within a doped matrix included in the medical device, such as a portion of a guidewire. In another example, one or more filaments are laid along a portion of the medical device, such as a guidewire or coated guidewire, and then covered with a polymer, sandwiching the filament or filaments between the guidewire or coated guidewire and the polymer coating. In these embodiments, the filaments can be disposed axially along the portion of the medical device or helically wrapped around the portion of the medical device. In these embodiments, the filaments can be relatively short filaments with a relatively small diameter, such as filaments having a length of about 10 cm or less and a diameter of about 25 microns or less. When made from stainless steel, this provides a filament with a mass of about 0.4 mg. When formed from stainless steel with an appropriate and desirable ultimate tensile strength as described herein, such as less than about 200 KSI, these filaments can serve as effective artifact-generating markers as described herein. In these embodiments, when multiple filaments are used in the same medical device, it is believed to be important to space the filaments from one another in the medical device so that a gap is formed between each pair of filaments, thereby avoiding the formation of conductive paths between the filaments. In these embodiments, a gap of at least a few thousandths of an inch is believed to be suitable. In all embodiments involving filaments, the filaments can have a round cross-sectional profile or a flat cross-sectional profile, such as a square or rectangular cross-sectional profile.

[0063] Described herein are various methods of manufacturing medical devices, imaging methods, and performing interventional medical procedures. The methods described herein are shown and described as a series of acts, but are not limited by the order of the acts, except as indicated, as some acts may occur in different orders and / or simultaneously with other acts described herein according to these methods.

[0064] FIG. 6 is a schematic diagram of an example method 1000 for manufacturing a medical device. A first step 1002 involves selecting a medical device precursor having a body member with a proximal end and a distal end. Another step 1004 involves selecting a marker stock member formed from annealed stainless steel. Another step 1006 involves separating a portion of the marker stock member from the remainder of the marker stock member to form a marker comprising annealed stainless steel. Another step 1008 involves attaching the marker to the body member in a manner that works the stainless steel of the marker, such that upon completion of the attaching step 1008, the marker comprises work-hardened stainless steel. In other words, step 1008 involves attaching the marker to the body member in a manner that increases the ultimate tensile strength of the stainless steel of the marker.

[0065] Step 1002 of selecting a medical device precursor can be accomplished by identifying a medical device or medical device to which it is desirable to attach a marker for the purpose of using the medical device in magnetic resonance imaging. The medical device can be any suitable medical device or precursor to such a medical device. Examples of suitable medical devices include guidewires, catheters, needles, sheaths, snares, and other suitable interventional medical devices. Implantable medical devices such as stents, frames, valves, filters, occluders, and other devices can also be selected in this step.

[0066] Step 1004 of selecting a marker stock member can be accomplished by identifying an annealed stainless steel marker stock member having dimensions suitable for use as a marker for the medical device identified in step 1002, which will be modified in subsequent steps. For this step in this example method, it is important that the stainless steel be annealed because the cold working completed in attachment step 1008 provides the necessary processing to create the desired visual artifact. Examples of suitable types of marker stock members include rods, ribbons, bars, and tubular members. The specific type of marker stock member selected in a particular method of manufacturing a medical device will depend on various considerations, including the nature of the medical device being manufactured. For example, if the medical device being manufactured includes an elongated member, such as a rod, strut, or other elongated member, a tubular marker stock member can be selected to allow a marker formed from the marker stock member to be circumferentially positioned around the rod or other elongated member of the medical device. Similarly, if the medical device being manufactured includes a passageway in a wall member, for example, the rod marker stock member can be selected to allow a marker formed from the marker stock member to be placed in the passageway of the medical device as a plug.

[0067] Step 1006 of separating a portion of the marker stock member from the remainder of the marker stock member may be accomplished by cutting the portion of the marker stock member from the remainder of the marker stock member, such as by laser cutting or other suitable technique. For this step in this example method, it is important that the separation be performed in a manner that does not alter the stainless steel of the portion of the marker stock member that is being separated from the remainder of the marker stock member. For this reason, laser cutting and similar techniques are believed to be preferred, and for the same reason, crimping, bending, and other cold working techniques are not believed to be preferred.

[0068] Attaching the marker to the body member in step 1008 by working the stainless steel of the marker can be accomplished by any suitable method of cold working the marker formed in separating step 1006, such that the stainless steel of the marker comprises work-hardened stainless steel upon completion of attaching step 1008. Examples of suitable cold working techniques include crimping, swaging, hammering, pressing, pinning, and dimpling. The technique selected for a particular method of manufacturing a medical device will depend on various considerations, including the nature of the medical device being manufactured and the nature of the marker formed in step 1006. For this particular method, for example, if the marker formed in step 1006 is a tubular member defining a lumen or a member defining a partial circumference, such as a C-shaped member, and the medical device being manufactured includes an elongated member, such as a rod, strut, or other elongated member, the marker can be attached to the body member of the medical device precursor by circumferentially positioning the marker around the elongated member of the medical device and crimping the marker to the elongated member. Also, if the marker formed in step 1006 is a rod, plug, or other non-lumen-defining member, and the medical device being manufactured includes a wall member or other portion that defines a passageway, the marker can be attached to the body member of the medical device precursor by forcing, driving, or otherwise forcing the marker into the passageway.

[0069] Regardless of the technique selected for step 1008 in a method according to a particular embodiment, it is believed important that step 1008 of attaching the marker to the body member be performed such that, upon completion of step 1008, the stainless steel of the marker has an ultimate tensile strength of about 100 KSI to about 225 KSI. Furthermore, the inventors have determined that it is advantageous to perform step 1008 until the stainless steel of the marker has an ultimate tensile strength of about 150 KSI to about 200 KSI. Furthermore, the inventors have determined that it is advantageous to perform step 1008 until the stainless steel of the marker has an ultimate tensile strength of about 170 KSI to about 200 KSI. Furthermore, the inventors have determined that it is advantageous to perform step 1008 until the stainless steel of the marker has an ultimate tensile strength of about 172 KSI to about 197 KSI. Furthermore, the inventors have determined that it is advantageous to perform step 1008 until the stainless steel of the marker has an ultimate tensile strength of about 187 KSI to about 191 KSI. Additionally, the inventors have determined that it is advantageous to perform step 1008 until the stainless steel of the marker has an ultimate tensile strength of about 189 KSI.

[0070] To determine whether step 1008 has been performed to an adequate extent, the ultimate tensile strength of the marker can be determined in any suitable manner. For example, a hardness determination can be made, such as determining HV Vickers hardness or other suitable hardness, and then a correlation to the ultimate tensile strength can be performed using a known conversion factor. This approach can be used to evaluate the ultimate tensile strength of the marker in medical devices and methods according to embodiments. It should be noted that if the marker must be removed from the medical device to determine the ultimate tensile strength of the marker, the removal should be done in a manner that does not introduce additional processing into the stainless steel of the marker. That is, the removal should be done in a manner that does not itself increase the ultimate tensile strength of the marker.

[0071] FIG. 7 is a schematic diagram of another example method 1100 of manufacturing a medical device. An initial step 1102 involves selecting a medical device precursor having a body member with a proximal end and a distal end. Another step 1104 involves selecting a marker stock member formed from stainless steel. Another step 1106 involves separating a portion of the marker stock member from the remainder of the marker stock member to form a marker. Another step 1108 involves identifying a desired ultimate tensile strength for the marker. Another step 1110 involves cold working the marker until the marker has a marker ultimate tensile strength that is substantially the same as the ultimate ultimate tensile strength identified in step 1108. Another step 1112 involves attaching the marker to the body member in a manner that does not substantially work the stainless steel of the marker, so that upon completion of the attaching step 1112, the ultimate tensile strength of the marker is substantially the ultimate tensile strength identified in step 1108.

[0072] Step 1102 of selecting a medical device precursor can be accomplished by identifying a medical device or medical device to which it is desirable to attach a marker for the purpose of using the medical device in magnetic resonance imaging. The medical device can be any suitable medical device or precursor to such a medical device. Examples of suitable medical devices include guidewires, catheters, needles, sheaths, snares, or other suitable interventional medical devices. Implantable medical devices, such as stents, frames, valves, filters, occluders, and other devices, can also be selected in this step. Medical device precursors can include any structural members that can precede a completed medical device in a method of manufacturing a medical device, such as frames, wires, rods, sheaths, and other suitable structural members.

[0073] Step 1104 of selecting a marker stock member can be accomplished by identifying a stainless steel marker stock member having suitable dimensions for use as a marker for the medical device identified in step 1102, which will be modified in a subsequent step. For this step in the example method, the stainless steel can be annealed, since the cold working completed in the subsequent step 1110 provides the necessary processing to create the desired visual artifact. Importantly, however, for this step in the example method, the stainless steel can be unannealed, as long as it has a maximum tensile strength that allows the processing input via cold working to achieve the desired final maximum tensile strength in a subsequent step. Examples of suitable types of marker stock members include rods, ribbons, bars, and tubular members. The specific type of marker stock member selected in a particular method of manufacturing a medical device will depend on various considerations, including the nature of the medical device being manufactured. For example, if the medical device being manufactured includes an elongated member, such as a rod, strut, or other elongated member, a tubular marker stock member can be selected to allow a marker formed from the marker stock member to be positioned circumferentially around the rod or other elongated member of the medical device. Similarly, if the medical device being manufactured includes a passageway in a wall member, for example, a rod marker stock member can be selected to allow a marker formed from the marker stock member to be positioned in the passageway of the medical device. Examples of suitable marker stock member types and dimensions include those described above for the first example method of manufacturing a medical device.

[0074] Step 1106 of separating a portion of the marker stock member from the remainder of the marker stock member can be accomplished by cutting the portion of the marker stock member from the remainder of the marker stock member, such as by laser cutting or other suitable technique. For this step in this example method, separation can be accomplished by processing the stainless steel of the portion of the marker stock member that is separated from the remainder of the marker stock member. For this reason, laser cutting and similar techniques are believed to be preferred, and for the same reason, crimping, bending, and other cold working techniques are also believed to be suitable. Importantly, however, if the technique selected for this step processes the stainless steel of the portion of the marker stock member that is separated from the remainder of the marker stock member, the portion of the marker stock member that is separated from the remainder of the marker stock member should have a maximum tensile strength that is less than the specified ultimate maximum tensile strength so that the subsequent step 1110 can process the marker toward achieving the ultimate maximum tensile strength.

[0075] In step 1108, which identifies a desired ultimate tensile strength for the marker, the ultimate tensile strength selected need only exceed the starting ultimate tensile strength of the marker stock member and be achievable by the cold working performed on the marker in step 1110. As described herein, it is believed important that the ultimate tensile strength selected be between about 100 KSI and about 225 KSI. The inventors have determined that an ultimate tensile strength of between about 150 KSI and about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of between about 170 KSI and about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of between about 172 KSI and about 197 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of between about 187 KSI and about 191 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 189 KSI may be advantageous.

[0076] Step 1110 of cold working the marker until the marker has a marker maximum tensile strength substantially the same as the final maximum tensile strength determined in step 1108 can be accomplished using any suitable cold working technique. Examples of suitable cold working techniques include crimping, swaging, striking, folding, bending, forming, rolling, knurling, cold forging, finish punching, riveting, stacking, coining, peening, punching, parting, deep drawing, drawing, and dimpling. Regardless of the technique selected for step 1110 in a method according to certain embodiments, it is believed important that step 1110 of cold working the marker be performed so that the stainless steel of the marker has a maximum tensile strength of about 100 KSI to about 225 KSI upon completion of step 1110. Furthermore, the inventors have determined that it is advantageous to perform this step 1110 until the stainless steel of the marker has a maximum tensile strength of about 150 KSI to about 200 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1110 until the stainless steel marker has an ultimate tensile strength of about 170 KSI to about 200 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1110 until the stainless steel marker has an ultimate tensile strength of about 172 KSI to about 197 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1110 until the stainless steel marker has an ultimate tensile strength of about 187 KSI to about 191 KSI. Furthermore, the inventors have determined that it is advantageous to perform step 1110 until the stainless steel marker has an ultimate tensile strength of about 189 KSI.

[0077] Step 1112 of attaching the marker to the body member in a manner that does not substantially work the stainless steel of the marker can be accomplished using any suitable attachment technique that does not further cold work the marker. Examples of suitable techniques include adhesively adhering the marker to the body member of the medical device precursor, welding the marker to the body member, bonding, reflowing a polymer around the marker, potting, and other similar techniques.

[0078] FIG. 8 is a schematic diagram of another example method 1200 of manufacturing a medical device. An initial step 1202 involves selecting a medical device predecessor having a body member with a proximal end and a distal end. Another step 1204 involves selecting a marker stock member formed from stainless steel having a starting maximum tensile strength. Another step 1206 involves separating a portion of the marker stock member from the remainder of the marker stock member to form a marker. Another step 1208 involves identifying a desired final maximum tensile strength for the marker. Another step 1210 involves cold working the marker until it has a marker maximum tensile strength that exceeds the starting maximum tensile strength but is less than the final maximum tensile strength identified in step 1208. Another step 1212 involves attaching the marker to the body member in a manner that works the stainless steel of the marker so that, upon completion of the attaching step 1212, the marker's maximum tensile strength is substantially the maximum tensile strength identified in step 1208.

[0079] The step 1202 of selecting a medical device precursor can be accomplished by identifying a medical device or medical device to which it is desirable to attach a marker for the purpose of using the medical device in magnetic resonance imaging. The medical device can be any suitable medical device or precursor to such a medical device. Examples of suitable medical devices include guidewires, catheters, needles, sheaths, snares, and other suitable interventional medical devices. Implantable medical devices such as stents, frames, valves, filters, occluders, and other devices can also be selected in this step.

[0080] Step 1204 of selecting a marker stock member can be accomplished by identifying a stainless steel marker stock member having dimensions suitable for use as a marker for the medical device identified in step 1202, which will be modified in subsequent steps. For this step in the example method, the stainless steel can be annealed, since the cold working completed in subsequent steps 1210 and 1212 provides the necessary processing to create the desired visual artifact. Importantly, however, for this step in the example method, the stainless steel can be unannealed, as long as it has a maximum tensile strength that allows the processing input via cold working to achieve the desired final maximum tensile strength in subsequent steps. The marker stock member selected has a starting maximum tensile strength. Examples of suitable types of marker stock members include rods, ribbons, bars, and tubular members. The specific type of marker stock member selected in a particular method of manufacturing a medical device will depend on various considerations, including the nature of the medical device being manufactured. For example, if the medical device being manufactured includes an elongated member, such as a rod, strut, or other elongated member, a tubular marker stock member can be selected to allow a marker formed from the marker stock member to be positioned circumferentially around the rod or other elongated member of the medical device. Similarly, if the medical device being manufactured includes a passageway in a wall member, for example, a rod marker stock member can be selected to allow a marker formed from the marker stock member to be positioned in the passageway of the medical device. Examples of suitable marker stock member types and dimensions include those described above for the first example method of manufacturing a medical device.

[0081] Step 1206 of separating a portion of the marker stock member from the remainder of the marker stock member can be accomplished by cutting the portion of the marker stock member from the remainder of the marker stock member, such as by laser cutting or other suitable technique. For this step in this example method, the separation can be accomplished by processing the stainless steel of the portion of the marker stock member that is separated from the remainder of the marker stock member. For this reason, laser cutting and similar techniques are believed to be preferred, and for the same reason, crimping, bending, and other cold working techniques are also believed to be suitable. Importantly, however, if the technique selected for this step processes the stainless steel of the portion of the marker stock member that is separated from the remainder of the marker stock member, the portion of the marker stock member that is separated from the remainder of the marker stock member should have a maximum tensile strength that is less than the specified ultimate maximum tensile strength so that subsequent steps 1210 and 1212 can process the marker toward achieving the ultimate maximum tensile strength.

[0082] In step 1208, which identifies a desired ultimate tensile strength for the marker, the ultimate tensile strength selected need only exceed the starting ultimate tensile strength of the marker stock member and be achievable by the cold working performed on the marker in steps 1210 and 1212. As described herein, it is believed important that the ultimate tensile strength selected be between about 100 KSI and about 225 KSI. The inventors have determined that an ultimate tensile strength of between about 150 KSI and about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of between about 170 KSI and about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of between about 172 KSI and about 197 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of between about 187 KSI and about 191 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 189 KSI may be advantageous.

[0083] Step 1210 of cold working the marker until it has a marker maximum tensile strength that exceeds the starting maximum tensile strength of the marker stock member but less than the final maximum tensile strength identified in step 1208 can be accomplished using any suitable cold working technique. Examples of suitable cold working techniques include crimping, swaging, striking, folding, bending, forming, rolling, knurling, cold forging, finish stamping, riveting, stacking, coining, peening, punching, parting, deep drawing, drawing, and dimpling. Regardless of what technique is selected for step 1210 in a method according to certain embodiments, it is believed important that step 1210 of cold working the marker be performed such that upon completion of step 1210, the stainless steel of the marker has a maximum tensile strength that is less than the final maximum tensile strength identified in step 1208. Although not essential given the effect of step 1212 on the ultimate tensile strength of the marker stainless steel, step 1210 can be performed so that the marker stainless steel has an ultimate tensile strength of about 100 KSI to about 225 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1210 until the marker stainless steel has an ultimate tensile strength of about 150 KSI to about 200 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1210 until the marker stainless steel has an ultimate tensile strength of about 170 KSI to about 200 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1210 until the marker stainless steel has an ultimate tensile strength of about 172 KSI to about 197 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1210 until the marker stainless steel has an ultimate tensile strength of about 187 KSI to about 191 KSI. Furthermore, the inventors have discovered that, particularly in methods where the ultimate tensile strength determined in step 1208 is about 189 KSI, it is advantageous to perform this step 1210 until the marker stainless steel has an ultimate tensile strength of about 187 KSI to about 191 KSI.

[0084] Attaching the marker to the body member in step 1212 by working the stainless steel of the marker can be accomplished by any suitable method of cold working the marker formed in separating step 1206 so that, upon completion of attaching step 1212, the stainless steel in the marker has a maximum tensile strength that is substantially the maximum tensile strength identified in step 1208. Examples of suitable cold working techniques include crimping, swaging, and hammering. The technique selected for a particular method of manufacturing a medical device will depend on various considerations, including the nature of the medical device being manufactured and the nature of the marker formed in step 1206. For example, if the marker formed in step 1206 is a tubular member defining a lumen and the medical device being manufactured includes an elongated member such as a rod, strut, or other elongated member, the marker can be attached to the body member of the medical device precursor by circumferentially positioning the marker around the elongated member of the medical device and crimping the marker to the elongated member. Also, if the marker formed in step 1206 is a rod, plug, or other non-lumen-defining member, and the medical device being manufactured includes a wall member or other portion that defines a passageway, the marker can be attached to the body member by forcing the marker into the passageway by pushing, driving, or otherwise forcing the marker into the passageway.

[0085] Regardless of the technique selected for step 1212 in a method according to a particular embodiment, it is believed important that step 1212 of attaching the marker to the body member be performed such that the stainless steel of the marker has an ultimate tensile strength of about 172 KSI to about 197 KSI upon completion of step 1212. The inventors have determined that it is advantageous to perform this step 1212 until the stainless steel of the marker has an ultimate tensile strength of about 187 KSI to about 191 KSI. Furthermore, the inventors have determined that it is advantageous to perform this step 1212 until the stainless steel of the marker has an ultimate tensile strength of about 189 KSI.

[0086] The extent of work performed on the marker stainless steel in step 1212 depends on the extent of work performed on the marker stainless steel in step 1210 and the final maximum tensile strength determined in step 1208. The total work performed on the marker stainless steel in both steps 1210 and 1212 depends on the final tensile strength of the marker stock member selected in step 1204 and the final maximum tensile strength determined in step 1208. In certain embodiment methods in which a marker stock member is selected comprising annealed stainless steel, the inventors have determined that it is advantageous to perform the majority of the cold work required to achieve the final maximum tensile strength in step 1210, leaving only the required cold work to be completed in step 1212. For example, if the marker stock member selected in step 1204 comprises annealed 304 stainless steel, which has a final tensile strength of approximately 75 KSI, it may be advantageous to perform step 1210 until the marker stainless steel has a final tensile strength of at least 129 KSI. It may further be advantageous to perform step 1210 until the marker stainless steel has an ultimate tensile strength of at least 150 KSI. It may further be advantageous to perform step 1210 until the marker stainless steel has an ultimate tensile strength of at least 170 KSI. It may further be advantageous to perform step 1210 until the marker stainless steel has an ultimate tensile strength of at least 180 KSI in methods where the final ultimate tensile strength determined in step 1208 is between about 187 KSI and about 191 KSI. For these same methods, it may also be advantageous to perform step 1210 until the marker stainless steel has an ultimate tensile strength of at least 185 KSI.

[0087] FIG. 9 is a schematic diagram of another example method 1300 for manufacturing a medical device. An initial step 1302 includes selecting a medical device precursor having a body member with proximal and distal ends, a first surface, a second surface, a thickness, and defining a passageway extending from the first surface to the second surface. Another step 1304 includes selecting an annealed stainless steel plug. Another step 1306 includes cold working the plug to form a marker. Another step 1308 includes forcing the marker into the passageway. An optional additional step includes immobilizing the marker to the body member, such as by laser welding the marker to the body member. Another optional additional step includes grinding a surface of the marker to make it flush with the first surface of the body member. Another optional step includes grinding another surface of the marker to make it flush with the second surface of the bearing member. Another optional additional step includes polishing one or more surfaces of the marker.

[0088] To provide access to the passageway, a medical device precursor should be selected whose first surface defines a first opening to the passageway. In these methods, the passageway can extend only partially through the thickness. In some embodiments, a medical device precursor can be selected whose second surface defines a second opening to the passageway. In these methods, the passageway extends from the first surface to the second surface through the entire thickness.

[0089] 10 is a schematic diagram of another example method 1400 of manufacturing a medical device. A first step 1402 includes selecting a medical device precursor having a body member with proximal and distal ends, a first side, a second side, a thickness, and defining a passageway extending from the first side toward the second side. Another step 1404 includes selecting an annealed stainless steel plug. Another step 1406 includes cold working the plug to form a marker having an ultimate tensile strength of about 172 KSI to about 197 KSI. Another step 1408 includes forcing the marker into the passageway.

[0090] 11 is a schematic diagram of another example method 1500 of manufacturing a medical device. A first step 1502 involves separating a portion of marker stock from a marker stock member comprising annealed stainless steel. A further step 1504 involves cold working the portion or marker stock to form a marker having an ultimate tensile strength of about 172 KSI to about 197 KSI. A further step 1506 involves attaching the marker to a body member of a medical device precursor to form the medical device.

[0091] FIG. 12 is a schematic diagram of an example imaging method 2000. A first step 2002 involves selecting a medical device having a body member with a proximal end and a distal end, the body member including a marker attached thereto. The marker is formed from work-hardened stainless steel. Another step 2004 involves advancing the distal end of the medical device to a first location within the patient's body vessel until the marker is positioned at a second location within the body vessel. Another step 2006 involves scanning a portion of the body vessel including the first and second locations within the body vessel using a magnetic resonance scanner. Another step 2008 involves obtaining a magnetic resonance image of the portion of the body vessel, such that the image includes an artifact indicative of the presence of the marker within the portion of the body vessel. A single still image can be obtained for this step 2008. Optionally, this step 2008 can be repeated any desired number of times to obtain multiple magnetic resonance images that can be grouped together as a cine to indicate movement. Another step 2010 involves withdrawing the medical device from the body vessel.

[0092] In step 2002 of selecting a medical device, it is believed important that the stainless steel of the marker have an ultimate tensile strength of about 100 KSI to about 225 KSI. The inventors have determined that an ultimate tensile strength of about 150 KSI to about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 170 KSI to about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 172 KSI to about 197 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 187 KSI to about 191 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 189 KSI may be advantageous.

[0093] FIG. 13 is a schematic diagram of another example imaging method 2100. A first step 2102 involves selecting a medical device having a body member with a proximal end and a distal end, the body member including a stainless steel marker attached thereto. The marker has an ultimate tensile strength of about 172 KSI to about 197 KSI. Another step 2104 involves advancing the distal end of the medical device to a first location within the patient's body vessel until the marker is positioned at a second location within the body vessel. Another step 2106 involves scanning a portion of the body vessel including the first and second locations within the body vessel using a magnetic resonance scanner. Another step 2108 involves obtaining a magnetic resonance image of the portion of the body vessel such that the image includes an artifact indicative of the presence of the marker within the portion of the body vessel. Another step 2110 involves withdrawing the medical device from the body vessel.

[0094] FIG. 14 is a schematic diagram of an example method 3000 for performing an interventional medical procedure. A first step 3002 includes selecting a medical device having a body member with a proximal end and a distal end, the body member including a marker attached thereto. The marker is formed from work-hardened stainless steel. Another step 3004 includes advancing the distal end of the medical device to a first position within the patient's body vessel until the marker is positioned at a second position within the body vessel. Another step 3006 includes acquiring a magnetic resonance image of a portion of the body vessel showing the second position while the marker is positioned at the second position within the body vessel. Another step 3008 includes, during step 3006 of acquiring the magnetic resonance image of the portion of the body vessel, viewing an artifact in the image created by the presence of the marker. Another step 3010 includes manipulating the medical device based on the position of the artifact relative to the body vessel. Another step 3012 includes withdrawing the medical device from the body vessel.

[0095] In step 3002 of selecting a medical device, it is believed important that the stainless steel of the marker have an ultimate tensile strength of about 100 KSI to about 225 KSI. The inventors have determined that an ultimate tensile strength of about 150 KSI to about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 170 KSI to about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 172 KSI to about 197 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 187 KSI to about 191 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 189 KSI may be advantageous.

[0096] The step 3010 of manipulating the medical device is performed in a manner that achieves or contributes to achieving a desired clinical outcome of the method 3000 of performing an interventional medical procedure. Thus, the nature of the step 3010 of manipulating the medical device will depend on the nature of the medical device and the desired clinical outcome. Examples of suitable actions that may be performed for this step include, but are not limited to, advancing the medical device axially within the body vessel, rotating the medical device within the body vessel, radially expanding the medical device within the body vessel, and axially withdrawing a portion of the medical device to allow another portion of the medical device, or a second medical device associated with the medical device, to radially expand within the body vessel.

[0097] FIG. 15 is a schematic diagram of another example method 3100 for performing an interventional medical procedure. A first step 3102 includes selecting a medical device having a body member with a proximal end and a distal end, the body member including a stainless steel marker attached thereto. The marker has an ultimate tensile strength of about 172 KSI to about 197 KSI. Another step 3104 includes advancing the distal end of the medical device to a first location within the patient's body vessel until the marker is positioned at a second location within the body vessel. Another step 3106 includes acquiring a magnetic resonance image of a portion of the body vessel including the second location while the marker is positioned at the second location within the body vessel. Another step 3108 includes, during step 3106 of acquiring a magnetic resonance image of the portion of the body vessel, viewing an artifact in the image created by the presence of the marker. Another step 3110 includes manipulating the medical device based on the location of the artifact relative to the body vessel. Another step 3112 includes withdrawing the medical device from the body vessel.

[0098] The step 3110 of manipulating the medical device is performed in a manner that achieves or contributes to achieving a desired clinical outcome of the method 3100 of performing an interventional medical procedure. Thus, the nature of the step 3110 of manipulating the medical device will depend on the nature of the medical device and the desired clinical outcome. Examples of suitable actions that may be performed for this step include, but are not limited to, advancing the medical device axially within the body vessel, rotating the medical device within the body vessel, radially expanding the medical device within the body vessel, and axially withdrawing a portion of the medical device to allow another portion of the medical device, or a second medical device associated with the medical device, to radially expand within the body vessel.

[0099] FIG. 16 is a schematic diagram of another example method 3200 for performing an interventional medical procedure. A first step 3202 includes selecting a medical device having a body member with a proximal end and a distal end, the body member including a marker attached thereto. The marker is formed from work-hardened stainless steel. Another step 3204 includes advancing the distal end of the medical device to a first location within the patient's body vessel until the marker is disposed at a second location within the body vessel. Another step 3206 includes acquiring a magnetic resonance image of a portion of the body vessel including the second location while the marker is disposed at the second location within the body vessel. Another step 3208 includes determining a location of a portion of the medical device within the body vessel during step 3206 of acquiring a magnetic resonance image of the portion of the body vessel based at least in part on an artifact produced in the image by the presence of the marker. Another step 3210 includes manipulating the medical device within the body vessel. Another step 3212 includes withdrawing the medical device from the body vessel.

[0100] In step 3202 of selecting a medical device, it is believed important that the stainless steel of the marker have an ultimate tensile strength of about 100 KSI to about 225 KSI. The inventors have determined that an ultimate tensile strength of about 150 KSI to about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 170 KSI to about 200 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 172 KSI to about 197 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 187 KSI to about 191 KSI may be advantageous. Furthermore, the inventors have determined that an ultimate tensile strength of about 189 KSI may be advantageous.

[0101] The step 3210 of manipulating the medical device is performed in a manner that achieves or contributes to achieving a desired clinical outcome of the method 3200 of performing an interventional medical procedure. Thus, the nature of the step 3210 of manipulating the medical device will depend on the nature of the medical device and the desired clinical outcome. Examples of suitable actions that may be performed for this step include, but are not limited to, advancing the medical device axially within the body vessel, rotating the medical device within the body vessel, radially expanding the medical device within the body vessel, and axially withdrawing a portion of the medical device to allow another portion of the medical device, or a second medical device associated with the medical device, to radially expand within the body vessel.

[0102] FIG. 17 is a schematic diagram of another example method 3300 for performing an interventional medical procedure. A first step 3302 includes selecting a medical device having a body member with a proximal end and a distal end, the body member including a stainless steel marker attached thereto. The marker has an ultimate tensile strength of about 172 KSI to about 197 KSI. Another step 3304 includes advancing the distal end of the medical device to a first location within the patient's body vessel until the marker is positioned at a second location within the body vessel. Another step 3306 includes acquiring a magnetic resonance image of a portion of the body vessel including the second location while the marker is positioned at the second location within the body vessel. Another step 3308 includes determining a location of a portion of the medical device within the body vessel during step 3306 of acquiring a magnetic resonance image of the portion of the body vessel based at least in part on an artifact produced in the image by the presence of the marker. Another step 3310 includes manipulating the medical device within the body vessel. Another step 3312 includes withdrawing the medical device from the body vessel.

[0103] The step 3310 of manipulating the medical device is performed in a manner that achieves or contributes to achieving a desired clinical outcome of the method 3300 of performing an interventional medical procedure. Thus, the nature of the step 3310 of manipulating the medical device will depend on the nature of the medical device and the desired clinical outcome. Examples of suitable actions that may be performed for this step include, but are not limited to, advancing the medical device axially within the body vessel, rotating the medical device within the body vessel, radially expanding the medical device within the body vessel, and axially withdrawing a portion of the medical device to allow another portion of the medical device, or a second medical device associated with the medical device, to radially expand within the body vessel.

[0104] In all embodiments, any suitable stainless steel can be used for the required marker or marker stock stainless steel. The inventors have determined that austenitic stainless steels are particularly suitable for use in the markers and marker stock of the various medical devices and methods described herein. Furthermore, the inventors have determined that stainless steels including austenitic chromium-nickel alloys are particularly suitable for use in the markers and marker stock of the various medical devices and methods described herein. Furthermore, the inventors have determined that stainless steels including SAE International 300 series stainless steels are particularly suitable for use in the markers and marker stock of the various medical devices and methods described herein. In certain embodiments, the stainless steel used in the marker or marker stock includes SAE Type 301 stainless steel, SAE Type 302 stainless steel, SAE Type 303 stainless steel, SAE Type 304 stainless steel, SAE Type 304L stainless steel, SAE Type 304LN stainless steel, SAE Type 308 stainless steel, SAE Type 309 stainless steel, SAE Type 310 stainless steel, SAE Type 310S stainless steel, SAE Type 316 stainless steel, SAE Type 316L stainless steel, SAE Type 316Ti stainless steel, or SAE Type 321 stainless steel. The inventors have determined that SAE Type 304 stainless steel is particularly advantageous for use in the markers and marker stock of the various medical devices and methods described herein. Other stainless steels, such as ferritic stainless steels, can also be used for the required stainless steel marker or marker stock. [Example]

[0105] Example 1 - Ultimate tensile strength and artifact size Methods: Seven marker stock pieces, each comprising a stainless steel tubular member of known dimensions and ultimate tensile strength, were laser cut into 1 mm long tubular markers. Each marker was then attached to a Nitinol rod by circumferentially positioning the marker on the rod. The rod and marker assembly were then placed in an ASTM imaging phantom. The samples were scanned in a 1.5T Siemens Aera Scanner using two sequences: GRE-flip angle: 25, slice thickness: 8 mm, TR / TE: 100 / 10 ms (survey scan) Trufi - flip angle: 70, slice thickness: 8 mm, TR / TE: 3.4 / 1.6 ms (clinical)

[0106] MR images were acquired in all three imaging planes: sagittal, coronal, and transverse. Image artifact size was calculated for each plane.

[0107] result: Table 1 below reports the dimensions, weight and image artifact size of the stainless steel markers.

[0108] [Table 1]

[0109] The effect of UTS on image artifact size is clearly observed when comparing two markers with exactly the same mass but different UTS, i.e., Sample E (197 UTS, 1.16 mg) and Sample F (172 UTS, 1.16 mg). Both have the same dimensions and weight, but different UTS. For Sample E, which has the largest UTS value, the image artifact size is significantly higher.

[0110] The effect of mass on image artifact size can be determined by comparing Sample E (197 UTS, 1.16 mg) and Sample D (197 UTS, 1.06 mg). Although both have the same UTS, Sample E has a slightly larger mass than Sample D, i.e., 1.16 mg vs. 1.06 mg. Overall, image artifact size is larger for Sample E.

[0111] The effect of mass on image artifacts is particularly evident when comparing Sample F (172 UTS, 1.16 mg) and Sample A (189 UTS, 0.76 mg). While Sample F has a lower UTS compared to Sample A, Sample F has a significantly higher mass and therefore a larger image artifact size than Sample A.

[0112] Example 2 - Ultimate tensile strength and artifact size Methods: A set of unannealed markers was prepared by cutting 1 mm tubular markers from a piece of marker stock comprising cold-worked 304 stainless steel tubing with an ultimate tensile strength of 176 KSI.

[0113] To prepare the annealed markers, a marker stock piece comprising cold-worked 304 stainless steel tubing with an ultimate tensile strength of 176 KSI was first placed in an argon-filled stainless steel heat treatment vessel and furnace annealed at 1900°F for 2 hours. This produced a shiny, soft tube of the same dimensions with an estimated ultimate tensile strength of 75 KSI. Then, 1 mm long tubular markers were cut from the annealed marker stock piece.

[0114] An unannealed marker / rod assembly was prepared by placing a marker from the unannealed marker set onto a nitinol rod and gluing the marker to the rod.

[0115] An annealing marker / rod assembly was prepared by placing a marker from the annealing marker set on a nitinol rod and gluing the marker to the rod.

[0116] The marker / rod assemblies were then scanned side-by-side under MRI. Images from three scans, each comparing annealed and unannealed markers of the same length, with varying lengths between scans, are shown in Figures 18A, 18B, and 18C. The difference in artifact size between the cold-worked, unannealed, and annealed markers is evident in each of Figures 18A, 18B, and 18C.

[0117] Those skilled in the art will appreciate that, in view of the overall teachings of this disclosure, various modifications and alternatives to the examples described and illustrated may be developed. Accordingly, the particular arrangements of elements and steps disclosed are intended to be merely illustrative, rather than limiting, with respect to the scope of the invention, which is to be given the full scope of the appended claims and any and all equivalents thereof. [Explanation of symbols]

[0118] 100 Medical Devices 110 Main body member 112 proximal end 114 Distal end 116 Mandrel 118 Reinforcement member 120 lumen 122 marker 124 First Marker 126 Second Marker 128 Third Marker 130 Fourth Marker 132 outer sheath 200 Medical Devices 210 Main body member 212 proximal end 214 Distal end 216 Rod 218 Connector 222 Marker 224 First Marker 226 Second Marker 228 Third Marker 230 Fourth Marker 232 Outer sheath 240 First Distance 250 Second Distance 260 The Third Distance 310 Tubular members 312 Exterior 314 Lumen 400 Medical Devices 410 Main body member 412 proximal end 414 Distal end 416 Cannula 418 Lumen 420 Distal tip 422 cutting edge 424 Hub parts 426 Wall 428 Inside 430 Exterior 432 Passage 450 marker

Claims

1. 1. A medical device for use in an interventional procedure performed under magnetic resonance imaging, comprising: a body member; a marker attached to the body member and made of work-hardened stainless steel having an ultimate tensile strength of 100 KSI (689.476 MPa) to 225 KSI (1551.321 MPa); A medical device comprising:

2. The medical device of claim 1 , wherein the marker comprises a tubular member having an outer surface and defining a marker lumen.

3. The medical device of claim 2 , wherein the marker lumen defines a substantially circular cross-sectional shape.

4. The medical device of claim 2 , wherein the marker is crimped to the body member.

5. The medical device of claim 2 , wherein the marker is swaged onto the body member.

6. 6. The medical device of claim 1, wherein the ultimate tensile strength is between 150 KSI (1034.214 MPa) and 200 KSI (1378.952 MPa).

7. 6. The medical device of claim 1, wherein the ultimate tensile strength is between 170 KSI (1172.1092 MPa) and 200 KSI (1378.952 MPa).

8. 6. The medical device of any one of claims 1 to 5, wherein the ultimate tensile strength is between 172 KSI (1185.89872 MPa) and 197 KSI (1358.26772 MPa).

9. 6. The medical device of claim 1, wherein the ultimate tensile strength is between 187 KSI (1289.32012 MPa) and 191 KSI (1316.89916 MPa).

10. 6. The medical device of claim 1, wherein the ultimate tensile strength is 189 KSI (1303.10964 MPa).

11. The medical device of any one of claims 1 to 10, wherein the marker has a mass between 0.05 mg and 2.74 mg.

12. The medical device of any one of claims 1 to 11, wherein the marker has a mass between 0.1 mg and 1.37 mg.

13. further comprising an elongated member; the body member having an outer sheath member; The medical device of claim 1 , wherein the elongate member is slidably disposed within the outer sheath member.

14. 1. A medical device for use in an interventional procedure performed under magnetic resonance imaging, comprising: an outer sheath member; an elongate member slidably disposed within the outer sheath member; a tubular marker attached to one of the outer sheath member and the elongated member, the marker having a mass between 0.1 mg and 1.37 mg and made of work-hardened stainless steel having an ultimate tensile strength between 100 KSI (689.476 MPa) and 225 KSI (1551.321 MPa); A medical device comprising:

15. 1. A medical device for use in an interventional procedure performed under magnetic resonance imaging, comprising: an outer sheath member; an elongate member slidably disposed within the outer sheath member; a first marker attached to the outer sheath member and made of work-hardened stainless steel having an ultimate tensile strength of 100 KSI (689.476 MPa) to 225 KSI (1551.321 MPa), the first marker defining a first marker lumen; a second marker attached to the elongated member and made of work-hardened stainless steel having an ultimate tensile strength of 100 KSI (689.476 MPa) to 225 KSI (1551.321 MPa); A medical device comprising:

16. the marker is disposed about a portion of the body member; or the marker is a plug disposed within a hole, cavity, passageway, or void in the body member; 13. The medical device of claim 1, wherein the medical device has at least one other marker spaced apart from the marker, the marker and the at least one other marker being adapted to produce non-overlapping visual artifacts under magnetic resonance imaging.

17. 17. The medical device of claim 1, wherein the marker has a length of 2 mm or less.

18. 18. The medical device of claim 1, wherein the marker generates a visual artifact in an MRI image to determine the position of the medical device relative to the portion of the body canal through which the medical device has been advanced.

19. 19. The medical device of claim 16, wherein the markers are disposed about a portion of the body member.

20. The medical device of claim 19 , wherein the marker is a tubular member.

21. 20. The medical device of claim 19, wherein the marker defines a partial circumference such that it extends around only a portion of the circumference of the body member.

22. 22. The medical device of any one of claims 16 to 21, wherein the marker is a plug disposed within a hole, cavity, passageway, or void in the body member.

23. 23. The medical device of claim 16, further comprising at least one other marker spaced apart from the marker, the marker and the at least one other marker being adapted to produce non-overlapping visual artifacts under magnetic resonance imaging.

Images